Control of Valley Polarization of Exciton Bound on Plasma Induced Vacancies in MoS₂ Monolayer

Point defects are intrinsic to 2D materials and critically influence their optical and electronic properties. Controlling and exploiting the spin/valley properties of these defects is essential for unlocking advanced functionalities. In this study, we introduce sulfur vacancies in MoS₂ monolayer using Ar⁺ plasma irradiation combined with subsequent hBN encapsulation, enabling stable defect-bound exciton emission with 20 meV linewidth, and finite valley polarization of the order of ≈10%. Using photoluminescence spectroscopy under magnetic fields and electrostatic doping, we reveal that the valley polarization of defect-bound excitons can be controlled by the relative energy position of the Fermi level and the defect states within each valley. By combining tuning gate voltage and magnetic field amplitude, we achieve continuous modulation of valley polarization from −30% to +50%. These findings provide fundamental insights into defects engineering and valley control in 2D semiconductors, offering new strategy for the development of the next generation of optoelectronic devices.